Keywords logistics pipeline magnetic grinding rotating magnetic field reciprocating magnetic field
Put the workpiece in the middle of the magnetic field and keep the relative pole and pole of the workpiece at a certain distance. When the workpiece moves relative to the magnetic pole, the magnetic abrasive particles will grind the surface of the workpiece.
With the development of science and technology, the stress state of magnetic abrasive particles in the grinding process of atomic energy in the semiconductor industry is shown in the figure industry, aerospace industry, biochemical industry, medical equipment industry, and food machinery industry. Claim.
For example, in the semiconductor industry, containers and pipelines that transport high-purity gases, and high-purity pipelines that transport ultrapure water in the atomic energy industry require that the inner wall surface roughness be less than that of the feet. The pipeline requires a high cleanliness pipeline, in which the inner surface roughness is required to be smaller than that of the feet.
These requirements are difficult to meet for rolling pipelines and non-decorative welded pipelines, and it is necessary to increase the processing procedures to process the inner surface.
The abrasive grain is a magnetic abrasive grain close to the surface of the workpiece in the processing area.
Under the action of the magnetic field, the magnetic abrasive particles are subjected to a force of Fx along the direction of the magnetic line of force and a force along the direction of the magnetic equipotential line.
At the same time, the magnetic abrasive particles are in contact with the surface of the workpiece to produce cutting resistance along the normal direction of the workpiece surface. The tangential resistance generated by the relative movement of the abrasive particles and the surface of the workpiece can prevent the abrasive particles from flowing out of the processing area, which ensures The normal magnetic field force of the grinding process can be expressed as a schematic diagram of the volumetric magnetic grinding of the magnetic abrasive particles in the introduction of the internal surface magnetic grinding.
Put the magnetic abrasive grains in the magnetic field, the magnetic abrasive grains in the magnetic field will point the strength of the magnetic field along the direction of the magnetic line of force. The magnetic field gradient of the magnetic susceptibility of the magnetic abrasive grains in the and directions is determined by the coordinates of the lines of magnetic force and magnetic equipotential. (2) It can be seen that the force of the magnetic field is proportional to the volume of the magnetic particles and the magnetic field strength and magnetic field gradient of the magnetic particles.
The requirements of the grinding movement diagram of the magnetic grinding scheme. The National Education Commission doctorate special research funded project 26 received the first draft. The revised draft received. The grinding movement includes two aspects: trajectory and speed.
The trajectory of the grinding movement is one of the important factors that determine the surface roughness of the workpiece to be polished.
Magnetic grinding that only achieves a monotonous grinding trajectory will produce circumferential circles on the inner surface of the workpiece. Secondly, it cannot fully use selective material removal to obtain the required surface quality more economically. Again, in the stainless steel logistics pipelines such as Magnetic Research Year Wang Yan The rotating magnetic field of the surface magnetic grinding design can reach the foot, but can not meet the technical requirements of the foot.
Therefore, it is absolutely necessary to study the excitation mechanism that can realize complex grinding trajectories and fully explore the process capability of magnetic grinding.
The pipeline used in this subject is stainless steel. The original surface roughness of the rolled pipeline is about Ra, and the length of the plant is around. The length of the pipe is or because 31 stainless steel is a non-magnetic material. Compared with the processing of ferromagnetic materials, the gap size is large. The magnetic resistance in the magnetic circuit of the inner surface machining is much larger. To obtain high magnetic induction intensity in the grinding area, it is not competent to use a permanent magnet excitation mechanism with a small volume and weight, and electromagnetic coil excitation must be used.
Therefore, the volume and weight of the entire excitation device are relatively large. The pipe is a thin-walled slender part. The high-speed rotation will cause the pipe deflection, vibration and noise due to the centrifugal force caused by the eccentric mass. The processing cannot be performed normally. From the above analysis, we can see that the pipe And the excitation device is not suitable for high-speed rotation, then the relative motion between the magnetic abrasive particles required for grinding and the surface of the workpiece must be provided by another method.
The schematic diagram of the magnetic field excitation device for generating a rotating magnetic field in an electromagnetic way is shown in the figure. The excitation mechanism of the rotating magnetic field is similar to the stator structure of a three-phase motor, except that each phase winding is no longer distributed circumferentially with multiple slots, but is concentratedly wound around the core. The magnetic poles are evenly distributed on the same circular cross section.
The rotating magnetic field only provides relative circumferential motion, and cannot produce complex and non-directional grinding trajectories, so the crank-slider mechanism has to be used to provide axial reciprocating motion.
Up to now, the problem of the grinding trajectory of the magnetic grinding on the inner surface of the pipeline has not yet been well solved. It is meaningful to study the complex relative movement of the magnetic abrasive particles and the working surface by electromagnetic excitation.
The power is not enough to overcome the friction to drive the magnetic brush. The magnetic brush appears to be stationary. When the relative displacement is large enough, the magnetic driving force can overcome the friction, thereby driving the magnetic brush, and the magnetic brush appears to follow.
The essence of this hysteresis is magnetoresistive driving, and the rate of change of magnetic permeability determines the magnetic driving force.
The amount of hysteresis is related to the axial dimension of the magnetic pole. This point, which is about the axial dimension, is very important for achieving complex grinding trajectories. This factor must be considered in determining the amplitude of the reciprocating motion of the magnetic pole.
The schematic diagram of the rotating magnetic field excitation mechanism in the figure moves the fixed magnetic pole of the workpiece to reciprocate, and it is found that the amplitude of the reciprocating motion of the magnetic pole relative to the workpiece is inconsistent with the amplitude of the magnetic brush relative to the workpiece.
When the amplitude of the reciprocating motion of the magnetic pole is less than a certain value, the magnetic brush does not produce relative motion with the workpiece. When the amplitude of the reciprocating motion of the magnetic pole is a relatively large value, the relative motion of the magnetic brush and the workpiece occurs, but the amplitude is less than the amplitude of the magnetic pole motion.
This property is similar to the hysteresis loop, as shown in the figure, when the relative displacement of a magnetic pole and a magnetic brush determines the rate of change of magnetic permeability.
When the relative displacement is small, the relationship between the magnetic pole of the magnetic drive pattern and the displacement of the magnetic brush, which is determined by the permeability change rate, is one of the important aspects of the grinding motion.
It not only has a great impact on the efficiency of the grinding work, but also on the quality of the grinding workpiece, so the following requirements are placed on the speed of the grinding movement.
The speed of the grinding movement should be uniform, even if it is not uniform, the difference between the maximum and minimum speeds should be as small as possible.
The speed of the grinding movement should not be too high, too high will cause the system temperature to rise too high and make the smoothness of the movement worse.
Production practice proves that under the same process conditions, the surface roughness obtained by the workpiece being ground decreases with the increase of the grinding movement speed.
The movement trajectory of the cylindrical surface is always synthesized by the circumferential rotary motion and the axial reciprocating linear motion.
When the frequency of the reciprocating linear motion is less than the circumferential rotation frequency, the grinding motion trajectory is a helical line whose helical angle changes periodically, and the grinding stripes formed on the surface of the workpiece are helical lines with two directions interlaced as shown in the figure.
In order to obtain a good surface roughness of the workpiece, the intersection angle of the helical lines in the two directions should be as close as possible when the frequency of the reciprocating linear motion is greater than the circumferential rotation frequency, and the grinding motion trajectory will be a wave-like curve as shown in FIG. 4b Similar to super-finished wave curves interlaced with each other, a good surface roughness can be obtained.
The use of reluctance drive causes the magnetic brush to produce a grinding motion trajectory similar to that shown in the figure, omitting the mechanism and device that realizes the axial reciprocating motion, and the grinding motion is realized entirely by electromagnetic means.
Turning Figure Grinding Stripe Schematic Diagram of Journal of Mechanical Engineering Vol.I Issue No. 2 Design of the Rotating Magnetic Field Principle of the Rotating Magnetic Field The design of the rotating magnetic field should draw on the high-speed large-step reluctance stepper motor diagram of the stator rotor structure similar to the switched reluctance motor A schematic diagram showing the principle of a three-phase large-step reluctance stepping motor.
The winding of the stator adopts the arrangement of the neighboring phases and the opposite poles of the opposite poles.
A three-phase, two-three-beat power supply is called one for one.
Second, each time two windings are energized, the direction of rotation is counterclockwise, and the step angle is still the same as if one C is pressed and the other is energized [the order is energized, and the motor rotates in the opposite direction.
The three magnetic poles are on one section, and the cadaver C is on the other section.
The axial distance is approximately the outer diameter of the workpiece. The excitation principle is shown in the figure. The three-phase pulse power supply is used for excitation.
The circumferential expansion of this pole arrangement is shown in the figure.
It can be seen that the magnetic brush makes one revolution along the circumferential direction of the inner surface, and the axis reciprocates three times.
Ignore the axial feed motion, in order to form cross-grinding stripes on the surface of the workpiece, the workpiece's optimal feed speed frequency in the circumferential direction) should be about the frequency of the magnetic field rotation, where the left and right are with the workpiece feed rotary motion and the rotating magnetic field The direction is related, the direction is the same, it should be less than the direction, and it should be greater than the optimal feed speed. It means that the direction of the grinding stripe produced by the magnetic brush at a certain point on each surface of the surface is different from the direction of the grinding stripe of the next rotation, and the area of ​​repetition is the smallest.
The schematic diagram of the reluctance stepper motor replaces the two-tooth rotor in the figure with non-ferromagnetic pipes and magnetic abrasives. See the three-phase double three-beat power supply method. The adjacent poles that are energized are opposite poles. The main magnetic flux circuit Will choose the circumferential direction.
In this way, a local magnetic flux dense area is formed in the circumferential direction, and the local magnetic flux dense area is stepped in the circumferential direction with the change in the winding energization, which is the circumferential rotational movement required for grinding.
The schematic diagram of the reciprocating magnetic field excitation mechanism is shown below. The influence of the three-phase double three-beat and three-phase six-beat excitation methods on the trajectory of the magnetic brush is discussed below.
The three-phase double-three-beat power-on method is that the magnetic brush rotates one turn after the power is turned on twice per phase in one step, and the trajectories of the two magnetic brushes are consistent.
As shown in the figure, due to the lag of the magnetic brush, each step of the magnetic brush is located in the latter pole of the two poles.
The generated trajectory wave height is about half of the cross-sectional distance, and the wavelength is unchanged.
However, the angle between the two directional trajectories becomes smaller.
Assuming that the frequency of the excitation pulse voltage is longevity, the frequency of the rotating magnetic field is related to the circumferential rotation frequency of the magnetic brush. The frequency of the axial reciprocating motion is discarded. The frequency of the rotating magnetic field is different. The excitation mechanism discussed above, the magnetic poles are distributed on the same circular cross-section, so the magnetic brush only moves in the circumferential direction. Inspired by the structure of the linear motor, the idea of ​​germinal magnetic poles in the axial dislocation is distributed. The magnetic poles are distributed at a certain distance. On the two circular cross-sections, the diagram of the magnetic brush trajectory is shown. The three-phase six-beat energizing method is designed for a year and month. After that, the magnetic brush makes one revolution, and the trajectories of the two magnetic brushes are the same.
Because there is a single-phase beat between each two-phase, the resulting trajectory is shown in the figure. The wave height of the trajectory is the same as that of the three-phase double-three beats, but it is closer to the wave shape, and the angle of the trajectory is unchanged.
The frequency of the rotating magnetic field and the motion of the magnetic brush is the same as that of three-phase double-three beats.
Excitation mechanism-a rotating magnetic field diagram Rotary magnetic field magnetic grinding test device physical photo magnetic brush duo Yue Yue, the daily habits of the side, the shape of the dead body, the scorpion and the armor, the daily practice mocks the scent of the magnetic brush before the cage map is discussed above All are for three-phase excitation. When the diameter of the tube is relatively large, more phases can be used to reduce the length of the high reluctance path between the poles or to improve the stability of the movement.
Test Results Processing Time t / Graph The relationship between surface roughness and processing time. The magnetic induction intensity obtained in the processing area by the permanent magnetic steel excitation of the Danzhou yue yuezhou light rice thick bowl is only about, so the electromagnetic coil is used to generate high magnetic induction intensity in the processing area, and the angle between the two adjacent magnetic poles is the magnetic pole and The coil core is formed by laminating electrical steel sheets.
The cross-sectional area of ​​the magnetic pole core iron in the direction of the magnetic flux is coiled with acoustic copper enameled wire and powered by a DC power supply.
For the magnetic grinding of non-magnetic materials in the test, there is a large reluctance gap between the two magnetic poles, and it is difficult to obtain a field strength comparable to that of magnetic materials.
In the actual design, many assumptions are made for the calculation without considering the strong magnetic leakage, that is, the magnetic flux is equal everywhere.
o The cross-sectional area of ​​the air gap is twice that of the pole ends, and it is a uniform magnetic field.
Using the excitation circuit shown in the figure, the maximum output voltage is the maximum current output. The relationship between the amount of material removed and the processing time is shown in the processing time diagram. The photo of the excitation circuit schematic diagram is not shown.
The test is conducted on a lathe, and the pipeline passes through the rotating magnetic field excitation mechanism.
The workpiece is a stainless steel rolled pipe, the outer diameter is an inner diameter of 30, the machining current is the magnetic induction intensity of the air medium in the machining gap, and the amount of magnetic abrasive is the surface roughness of the slurry and the change in material removal with time.
Observe the micro-morphology of the surface before and after processing with a high-resolution digital microscope.
The contour curve of the inner surface of the workpiece is measured by a surface roughness measuring instrument manufactured by Harbin Measuring Tool & Cutting Tool Factory.
One one, eight M moves.
(Zhao Gan has already made the old shape pseudo). Microscopic morphology and surface profile curve of the surface before magnetic grinding. Journal of Mechanical Engineering Vol.
Shanghai Jiaotong University, Shanghai Institute of Micromotors.
Micro special motor.
Shanghai Shanghai Science and Technology Press, Lin Qiwang, Zhao Youmin.
Magnetic circuit design principle.
Beijing Machinery Industry Press, is the old micrograph of Xi Yanzhao, the microscopic morphology and surface contour curve of the surface after magnetic grinding. The conclusion is due to the particularity of the inner surface of the pipeline. The pipeline and the excitation mechanism It is not suitable for high-speed rotary motion, and the rotating magnetic field generated by electromagnetic excitation provides a way to generate relative motion in a non-mechanical manner.
The design principle of the revolving magnetic field, that is, the basic action principle of the reluctance stepping motor, is introduced. A new type of revolving magnetic field that can realize complex grinding trajectories is designed. The revolving magnetic field generates wavy grinding stripes through the axial distribution of the magnetic poles, while completing the magnetic The circumferential rotation and axial reciprocating motion of the abrasive on the workpiece.
Finally, a rotating magnetic field magnetic grinding test was carried out with the pipeline.
References Yu Chengye.
Special processing technology.
Beijing Maozhibi National Defense Industry Press, Li Xuequan.
Research on the mechanism and technology of magnetic grinding of the inner surface of the logistics pipeline [Bo Chuang Kou Ding Wang Yan, female, born in 69, associate professor.
The main research direction is the research of special machining technologies such as magnetic grinding, laser machining and EDM.
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